RFID technology is, for example, used for communication between an RFID transponder and an RFID reading device. To this end, magnetic coupling is established, for example, between an antenna of the RFID transponder and an antenna of the reading device. Communication is performed, for example, by means of radio-frequency (RF) fields with a frequency in the order of MHz, for example at 13.56 MHz.
Passive RFID transponders communicate to the reading device by means of passive load modulation. On the other hand, ALM RFID transponders communicate to the reading device by generating a signal synchronous to an incoming field from the reading device. To this end, an oscillator signal of the RFID transponder needs to be repeatedly synchronized with a reader signal depending on the incoming field.
In order to reduce space consumption, RFID transponders with very small dimensions are required. Consequently, also the antenna of the RFID transponder is required to be very small. A drawback of such a small antenna is a reduction of a possible operating range, that is a maximum possible distance between the RFID transponder and the reading device that still allows for communication. An RFID transponder with a small antenna size may achieve only a limited load modulation amplitude at the reader. According to industrial standards, the load modulation amplitude must be higher than corresponding threshold values. Consequently, a reduction of the antenna size is limited in existing transponders.
Furthermore, the synchronization of the oscillator signal and the reader signal may require additional time during which no data transmission from the RFID transponder to the reading device may be possible. Thus, existing RFID transponders may be limited to transmission protocols that further reduce the achievable load modulation amplitude.
There is a need in the art to provide an improved concept for an RFID transponder providing instances for synchronization while keeping a high load modulation amplitude.